Prolonged culture in aerobic environments alters Escherichia coli H₂ production capacity

Growing interest in renewable energy continues to motivate new work on microbial biohydrogen production and in particular utilizing Escherichia coli a well-studied, facultative anaerobe. Here we characterize, for the first time the H₂ production rate and capacity, of E coli isolates from the 50 000th generation of the Long-Term Evolution Experiment. Under these reaction conditions, peak production rates near or above 5 mL per hour for 100 mL of lysogeny broth (LB media) was established for the ancestral strains and batch efficiencies between 0.15 and 0.22 mL H₂ produced per 1 mL LB media were achieved. All 11 isolates studied, which had been aerobically cultured in minimal media since 1988, exhibited a decreased H₂ production rate or capacity with many strains unable to grow under anaerobic conditions at all. The genomes of these strains have been sequenced and a preliminary analysis of the correlations between genotype and phenotype shows that mutations in gene ydjO are exclusively observed in the two isolates which produce H₂, potentially suggesting a role for this gene in the maintenance of wild type metabolic pathways in the context of diverse mutational backgrounds. These results provide hints towards uncovering new genetic targets for the pursuit of bacterial strains with increased capacity for H₂ production as well as a case study in speciation and the control of phenotypic switching.